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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

THE EARTHQUAKE ADVANCE THEORY                      179
are hi a lofty mountain region, it is doubtful if an uplift of many hundreds of feet would cause any notable addition to the snowfall. These mountains already rise so high, and form so continuous a barrier, that the damp ocean winds lose a great part of their vapor in rising over them, for the snow line lies between 2000 and 3000 feet. In the case of the smaller glaciers, for example Galiano and Atrevida Glaciers, an uplift might cause distinct increase in snowfall, for the mountains which supply them are lower. But even here, one could not imagine an uplift like the maximum of 47 feet in Yakutat Bay in 1899, or any uplift that was not measured in hundreds of feet, causing a sufficient increase in snowfall to cause such a notable advance and change in glacier condition.
Even making the extravagant supposition of an uplift of several hundred feet, there would not be sufficient increase in snowfall to bring about the spasmodic advance observed here unless with it there was some means of abruptly concentrating the effects of the snowfall on the glacier reservoirs. Such an uplift would also need to be assumed throughout a very great area, for the distance between the sources of the Marvine and the Hidden Glaciers is not less than 60 miles. The extravagant supposition of a mountain uplift of hundreds of feet throughout an area 60 miles in length, even if it were competent to account for the facts, would be proposing as a substitute an even more remarkable phenomenon than that which it is called upon to explain and one not indicated by the delicate seacoast register. Beside the extreme improbability of this hypothesis, even in its least extravagant form, we have the more convincing fact that the advance of the glaciers ceased as abruptly as it began. Were the advance due to uplift, its effects, at least in diminished form, should have continued. For these reasons we cannot entertain this theory.
A sudden advance of glaciers might conceivably be caused by a tilting of their valleys, but this hypothesis certainly cannot be applied to the Yakutat Bay advances, for there axe several fatal objections to it in addition to the improbability of a sufficient increase in grade to transform an uncrevassed glacier to broken condition, and to replace long stagnation by sudden advance. TKe first objection is the lack of evidence by observation. A change in grade sufficient to cause so great a change in glacier condition should certainly be noticeable, and we are unable to detect it. A second objection is the different directions pursued by the different advancing glaciers—some flowing southward, one eastward, and one westward. It would require complexity of breaking and inclination of a mountain region not only entirely without precedent, but, judging by our knowledge of earth changes, wholly impossible. Finally, even if we assumed the possibility of the change it would be necessary to assume also a return to approximately the former condition, for we have to explain not only a sudden advance, but a sudden cessation of advance.
Untenable Earthquake Hypotheses. The occurrence of the severe earthquakes of 1899 naturally led us to consider in what ways it might be possible for the transformation of the glaciers to be a response to these earthquakes, and four hypotheses have suggested themselves, three of which are easily disproved, while one is so supported by the facts that it is retained.
Of the three earthquake hypotheses that are discarded the first is that the changes in the glaciers are the result of breaking of the ice by the vigorous shaking either in 1899 or in some subsequent year. It strains the imagination to conceive of such a shaking as to break a glacier into impassable condition by such a cause, but waiving this, and